PM1044: A Novel Patient-derived Stem Cell Model of Restrictive Cardiomyopathy Exhibits Impaired Cardiomyocyte Relaxation Secondary to Increased Myocardial Calcium Sensitivity

Background: Restrictive Cardiomyopathy (RCM) is a rare disease characterized by profound, isolated defects in myocardial relaxation, normal or near-normal myocardial wall thickness, and preserved contractile function. Outcomes for patients with RCM are poor, with increased morbidity and mortality compared to other forms of cardiomyopathy. In some patients, RCM can be caused by genetic mutations, notably in genes encoding for components of the sarcomere. While many mutations have been described in RCM patients, the molecular and cellular mechanisms leading from these mutations to the patient’s physiological phenotype are poorly described. Hypothesis: Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) derived from RCM patients will recapitulate the myocardial relaxation defects seen in RCM and provide a novel in vitro model for investigating the molecular mechanisms underpinning this disease.

Methods: Induced pluripotent stem cells (iPSCs) were derived from a pediatric patient with RCM caused by a TNNT2 R94C mutation. CRISPR was used to correct the mutation, and cellular mechanics and calcium handling properties were compared to the patient line using a novel high-throughput traction-force imaging platform. Transcriptional profiles were compared using RNA-seq.

Results: RCM cells carrying the TNNT2 R94C mutation show increased calcium sensitivity leading to increased resting tension at baseline, as well as prolonged calcium kinetics leading to prolonged relaxation times. Gene expression profiling reveals changes in expression of ECM genes, which may further contribute to the impaired myocardial relaxation seen in RCM.

Conclusion: Patient-derived hiPSC-CMs from an RCM patient recapitulate the relaxation defects seen in RCM and highlight the central role of increased calcium sensitivity in impaired myocardial relaxation.